Touch display with RGB silicone buttons for Bus Pirate Ultra

This is the prototype display board for the next, and possibly final, revision of Bus Pirate “Ultra” v1. We went a bit wild, but we’re thrilled at the possibilities:

  • 2.8″ IPS LCD with capacitive touch display. The capacitive touch sensor is I2C based, so we added an I2C bus and interrupt pin to the flex connector
  • 2 silicone buttons with an RGB LED under each. The buttons are read through a TCA9534 I2C IO expander, basically a 5volt tolerant PCF8574 at half the price. The TCA9534 uses the same I2C bus as the capacitive touch sensor, and gets a dedicated interrupt signal on the flex connector
  • SK9822 RGB LEDs share an SPI bus with the LCD. The SK9822 runs at 5volts and uses a two pin protocol that can be driven by an SPI peripheral, but it doesn’t have a chip select pin so it can’t share an SPI bus with other slaves. We use a 74HCT573 as a level converter (3.3->5volts), and the 573’s latch pin as a pseudo chip select
  • The board is now powered from VUSB (5volts) and has a 3.3volt regulator
  • 6 additional IOs (routing in progress) from the unused pins of the TCA9534

A few tweaks to the schematic before we send off the PCBs:
*MISO on SPI should be jumpered. This leaves a disconnected pin between VUSB (5volts) and the 3.3volt logic pins
*Route unused IO pins to a header
*Run LCD backlight from VUSB

v1e is nearly complete and we’ll make a small batch of them soon, but probably immediately after spring festival. Feels free to hit us up on Twitter or check out the latest in the forum.

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